hey guys,

So my roomates 99 5.3 silvy's fuel pump gave out the other day. Its been whining quite loud for a few years now and it finally gave out. We bought a new pump, dropped the tank, swappyed the two, put on the new supplied connector and went to start it and truck would still not start.

What should we be looking for now? fuses, relays?

The truck will turn over but will not start. Also when key is on, we cant hear the fuel pump prime. is it that quiet? any ideas?

A new part is always a good part.

Put a test light in the connector at the fuel pump, turn on the key to 'run', test light should light for 2 seconds. If you have power and ground there, you still have a bad pump. You did buy an AC Delco or Delfi pump/sending unit assembly, right???? or you'll be doing this regularly with a cheep-o pump.

If you don't have power at the pump, then back track to the relay underhood in the electrical center....then fuse.

the pump was the 270 dollar job from autozone. he doesnt plan on keeping the truck for very long anyhow so he wasnt going to spend 500 on the gm one from the dealer.

The fuel gauge works when we "key on" so its looking like the pump is not broke. I know that its two different parts but im assuming since the whole thing is new, if 50% of it works then the other 50% would too. But just to be sure, we will check the power and ground in the connector.

Question on the fuse/relay. Would the fuse be blown first before the relay gets damaged? is the fuse there to protect the relay?

Ya, the fuse would blow first, the relay can handle much more amperage than the fuse. I was kind of going in line backtracking the electrical system to see where you possibly lost power (if that's the case). But easiest first is to check the fuse. *Suburbans would blow the ECM-B fuse and cause the fuel pump not to work, but the fix was to replace the pump and check the connector.*

Sounds like something didn't get plugged in. I think the fuel gauge is wired to the bucket. You should check to make sure the pump is plugged in.

his fuel pump has two connectors on the top. one for fuel pump, one for fuel gage. i guess there are two models. some have one connector, some have two. everything is plugged in

Second one is for the EVAP system.

then I would say a fuse. If you don't hear the pump come on when you turn the key then it is either bad or isn't getting power.

RT: so one connector is for the pump and the other is for the evap system? Do you know which one the fuel gauge is on? Cause the fuel gauge works.

Well we checked all the fuses today with a meter and they were all good. still cant get it to work. no daylight left so i guess we try again tomorrow. any other ideas?

if you checked all the fuses did you happen to check the power at the pump assembly?

Are you dropping the tank or pulling the bed off? If you are doing the bed then obviously you can check everything while it is completely hooked up.

after you get the power to the pump,or replace the pump, be sure and replace the fuel filter. If the old pump was howling, it may have been straining to get fuel to the injection.

we are dropping the tank :( we're doing it in the apartment parking lot so we're crawling aroudn in the snow.

Duro, how could a clogged filter affect the pump turning on and off?


**another piece of info we got was that the crank positioning sensor has an affect on the fuel pump relay. Aka if the sensors detect knock it will not allow the relay to work. If its a bad sensor then it could possibly cause the relay to not work. I think tomorrow we are going to jump the relay and see. we rewired everything today and still nothing.

Gotta love working out in the parking lots!!!

RT: so one connector is for the pump and the other is for the evap system? Do you know which one the fuel gauge is on? Cause the fuel gauge works.

Well we checked all the fuses today with a meter and they were all good. still cant get it to work. no daylight left so i guess we try again tomorrow. any other ideas?


The square connector with the blue retaining clip is the fuel pump connecton. The easyiest way to tell it's the pump + is when you turn on the ignition, the + is only on for 2 seconds, then turns off until the vehicle is started.

O'ya, pulling the bed is easier than dropping the tank

Just make sure you have more than 2 guys to do it....unless you are a big dude. Messed up my back trying that...but did get it back on.

A clogged filter makes the pump work much harder than it was designed to, the harder pumping eats the brass brushes in the pump motor

ALWAYS replace filter when replacing pump

Since you mention snow I'll guess you're up nawth, when all else fails check ALL connections and grounds for corrosion.... BTW did pump come with new connector??? If not check connector at tank, if it looks the least bit burnt replace it... NOW... you can get the connector seperately from NAPA.... connector burning is common with GM pumps... itty bitty terminals

In my vast experience with GM fuel pumps, the top of the tank module has a pass through connector that always corroded on mine. It requires replacement of the whole module. IIRC, it was less than $300 at GM.
Inspect where the inner harness from the pump plugs into the roof of the tank. That cavity should look brand new and the pins should be shiny. Over 3/4s of the ones I did were corroded there.

hey RT ill give you a call sometime today. what time is good for you?

When we key on, using a meter under the truck we had no power going to the plug. The plug on the harness is new so corrosion isnt the culprit. The fuses and relays are also good.

Does anyone know more about some control modual that links the crank positioning sensor and cam pos. sensor to the fuel pump relay. If either one is not happy it doesnt allow the relay to work.

it also has a new filter.

Anytime is fine today, it's kind of slow around here.

Are you sure the "supplied connector" was attached to the correct wires? And the crimps are good?

And remember, the voltage is only present for the first two seconds of key on, or steady while cranking. A jumper in place of the fuel relay will allow the 12Volt to be tested.

Just remember, Sparks + Gas fumes = Oh shit.

ya, i got some wiring info from rt. We re-crimped everything yesterday thinking it was a bad connection. We will test the relay even though we already swapped it with the horn relay and still nothing, but we'll test it anyway.

thanks for the spark tip lol

Update: Pump works finally!!! Turns out one of the ground straps didn't want to play nice. Glad it was something simple though. Thanks to everyone for helping